I. Technical Field
The present invention pertains generally to telecommunications, and particularly to fast hybrid ARQ (HARQ) protocols between mobile terminals and a radio network, including but not limited to HARQ protocols in a High Speed Uplink Packet Access (HSUPA) system such as that operated (for example) in a Universal Mobile Telecommunications System (UMTS) terrestrial radio access network (UTRAN).
II. Related Art and Other Considerations
In a typical cellular radio system, mobile terminals (also known as mobile stations and mobile user equipment units (UEs)) communicate via a radio access network (RAN) to one or more core networks. The user equipment units (UEs) can be mobile stations such as mobile telephones (“cellular” telephones) and laptops with mobile termination, and thus can be, for example, portable, pocket, hand-held, computer-included, or car-mounted mobile devices which communicate voice and/or data with radio access network.
The radio access network (RAN) covers a geographical area which is divided into cell areas, with each cell area being served by a base station. A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Each cell is identified by a unique identity, which is broadcast in the cell. The base stations communicate over the air interface (e.g., radio frequencies) with the user equipment units (UE) within range of the base stations. In the radio access network, several base stations are typically connected (e.g., by landlines or microwave) to a radio network controller (RNC). The radio network controller, also sometimes termed a base station controller (BSC), supervises and coordinates various activities of the plural base stations connected thereto. The radio network controllers are typically connected to one or more core networks.
The Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the Global System for Mobile Communications (GSM), and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology.
As wireless Internet services have become popular, various services require higher data rates and higher capacity. Although UMTS has been designed to support multi-media wireless services, the maximum data rate is not enough to satisfy the required quality of services.
In a forum known as the Third Generation Partnership Project (3GPP), telecommunications suppliers propose and agree upon standards for third generation networks and UTRAN specifically, and investigate enhanced data rate and radio capacity. One result of the forum's work is the High Speed Downlink Packet Access (HSDPA) for the downlink, which was introduced in 3GPP WCDMA specification Release 5. HSDPA features a high speed channel (HSC) controller that functions, e.g., as a high speed scheduler by multiplexing user information for transmission over the entire HS-DSCH bandwidth in time-multiplexed intervals (called transmission time intervals (TTI)). Since HSDPA uses code multiplexing, several users can be scheduled at the same time.
Concerning High Speed Downlink Packet Access (HSDPA) generally, see, e.g., 3GPP TS 25.435 V7.1.0 (Jun. 16, 2006), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; UTRAN Iub Interface User Plane Protocols for Common Transport Channel Data Streams (Release 7), which discusses High Speed Downlink Packet Access (HSDPA) and which is incorporated herein by reference in its entirety. Also incorporated by reference herein as being produced by the forum and having some bearing on High Speed Downlink Packet Access (HSDPA) or concepts described herein include: 3GPP TS 25.321 V7.1.0 (Jun. 23, 2006), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Medium Access Control (MAC) protocol specification (Release 7); 3GPP TS 25.331 V7.1.0 (Jun. 23, 2006), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Radio Resource Control (RRC); Protocol Specification (Release 7); 3GPP TS 25.425 V7.1.0 (Jun. 16, 2006), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; UTRAN Iur interface user plane protocols for Common Transport Channel data streams (Release 7); and 3GPP TS 25.433 V7.1.0 (Jun. 20, 2006), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; UTRAN Iub interface Node B Application Part (NBAP) signaling (Release 7).
The High Speed Downlink Packet Access (HSDPA) was followed by introduction of High Speed Uplink Packet Access (HSUPA) with its Enhanced Dedicated Channel (E-DCH) in the uplink in 3GPP WCDMA specification Release 6.
The new channels of HSDPA and HSUPA are designed to support IP-based communication efficiently, providing enhanced end-user performance and increased system capacity. Although originally designed for interactive and background applications, they provide as good or even better performance for conversational services than the existing circuit switched (CS) bearers.
E-DCH is dedicated uplink channel (from a user equipment unit (UE) to a Node-B) that has been enhanced for IP transmission. Enhancements include using a short transmission time interval (TTI); fast hybrid ARQ (HARQ) between mobile terminal and the Node-B (with soft combining); scheduling of the transmission rates of mobile terminals from the Node-B. In addition, E-DCH retains majority of the features characteristic for dedicated channels in the uplink.
E-DCH comes with several channels from each UE. For example, the DPCCH carries pilot symbols and parts of the outband control signaling. Remaining outband control signalling for the enhanced uplink, e.g., scheduling requests, is carried on the E-DPCCH, while the E-DPDCH carries the data transmitted using the enhanced uplink features.
In terms of the User Plane Radio Interface Protocol Architecture of HSUPA, the HARQ protocol and scheduling function belong to the Medium Access Control High Speed (MAC-hs) sublayer which is distributed across Node-B and the user equipment unit. Parameters of the protocols are configured by signaling in the control plane. This signaling is governed by Radio Resource Control (RRC) protocol. The service that is offered from RLC sublayer for point-to-point connection between a core network (CN) and the user equipment unit is referred to as a Radio Access Bearer (RAB). Each RAB is subsequently mapped to a service offered from the MAC layer. This service is referred to as a Logical Channel (LC).
In basic operation of HSUPA, a Node-B and user equipment unit perform an initial setting process for transmitting/receiving the E-DCH. Upon completion of setup, the user equipment unit informs the Node-B of scheduling information, e.g., information about transmission power of the UE from which uplink channel information can be known, information about the amount of data store in a buffer of the user equipment unit to be transmitted, and the like. The Node-B receives the scheduling information and determines whether and how to perform its own scheduling of the E-DCH for the user equipment unit (based on the scheduling information received from the user equipment unit). If it is possible to schedule the user equipment unit for the E-DCH, the Node-B generates scheduling allocation information which is sent to the user equipment unit. The scheduling information sent to the user equipment unit includes such information as data rate, transmission timing, etc. Upon receiving from the Node-B the scheduling information, the user equipment unit transmits the E-DCH using such scheduling information, and also transmits a E-DCH transport format combination indicator (E-TFCI) of the transmitted E-DCH.
Upon receiving a E-DCH, the Node-B determines whether any errors have occurred in the E-DCH or the TFRI. If an error occurs in either the TFRI or the E-DCH, the Node-B transmits a negative acknowledgement (NACK) to user equipment unit. On the other hand, if no error occur, the Node-B transmits an acknowledgement (ACK) to user equipment unit. The NACK and ACK are transmitted on the E-DCH HARQ Acknowledgement Indicator Channel (E-HICH). The NACK and ACK, and retransmissions attending receipt of a NACK, are the subject of the fast hybrid ARQ (HARQ) utilized between mobile terminal and the Node-B.
Hybrid ARQ technology in general is described in United States Patent Publication US 2004/0147236 and U.S. patent application Ser. No. 10/477,414, both entitled “METHOD AND SYSTEM OF RETRANSMISSION”, Soljanin E., Hybrid ARQ in Wireless Networks, presented at Wireless System Lab Seminar, Texas A&M University, April 2003, and DIMACS Workshop on Network Information Theory, March 2003; and, EP 1389847 A1; all of which are incorporated herein by reference.
The fast hybrid ARQ (HARQ) between mobile terminal and the Node-B for HSUPA involves a set of HARQ transmitting and receiving entities, located in Node B and UE respectively, which entities are also referred to as HARQ processes. The maximum number of HARQ processes per UE is usually predefined. These data flows from the user equipment unit to the Node-B can have different Quality of Services (QoS), e.g. delay and error requirements and may require a different configuration of HARQ instances.
The fast hybrid ARQ (HARQ) between mobile terminal and the Node-B for HSUPA also employs soft combining. That is, the Node-B temporarily stores data having an error and subsequently combines the stored data with a retransmitted portion of the corresponding data, the resultant combination hopefully thus being error free.
High Speed Uplink Packet Access (HSUPA), or at least E-DCH, is also discussed in one or more of the following (all of which are incorporated by reference herein in their entirety):
U.S. Patent Publication US 2005/0249120;
U.S. patent application Ser. No. 11/035,021, filed Jan. 14, 2005, entitled “UPLINK CONGESTION DETECTION AND CONTROL BETWEEN NODES IN A RADIO ACCESS NETWORK”;
U.S. Provisional Patent Application Ser. No. 60/659,429, filed Mar. 9, 2005, entitled “BLER MEASUREMENTS FOR OUTER-LOOP POWER CONTROL OF IDLE ENHANCED UPLINK CHANNELS”;
U.S. Provisional Patent Application Ser. No. 60/750,068, filed Dec. 14, 2005, entitled “DPDCH DESPREADING-ON-DEMAND (DOD) FOR WCDMA”;
U.S. Provisional Patent Application Ser. No. 60/804,687, filed Jun. 14, 2006, entitled “PACKET DISCARD TIMER FOR E-DCH”.
E-DCH has been specified with two configurable transmission time intervals (TTIs): a 10 ms TTI and a 2 ms TTI. The 2 ms TTI offers superior performance in many situations due to the lower latency and the possibility to utilize more HARQ retransmissions within a certain time bound.
Even if the 2 ms TTI is preferable in many situations, coverage may be limited. For example, if a protocol data unit (PDU) size of e.g. 336 bits (commonly used in WCDMA) needs to be transmitted, this corresponds to 168 kbps data rate (for which many networks may not be planned). However, by using several HARQ retransmissions, the effective data rate is reduced but the data can also be transmitted at the cell border (but with an increased delay). The HARQ round trip time (RTT) with a 2 ms TTI is 16 ms, which means that, e.g., 3 HARQ retransmissions (not including the original transmission) takes 2+3*16 ms=50 ms and corresponds to an efficient data rate of 168/4=42 kbps.
Since it is sometimes known in advance that several retransmissions will be needed, consideration has been given to performing autonomous retransmissions for the E-DCH. In the example above, the transmitter could (if it knows that three retransmissions are needed) perform all four transmissions in consecutive TTIs, thus completing the transmissions in 8 ms instead of 50 ms. For a discussion of autonomous retransmissions for an asynchronous HARQ as used in HSDPA, see WO/2005/109729, entitled “METHOD AND SYSTEM FOR PROVIDING AUTONOMOUS RETRANSMISSIONS IN A WIRELESS COMMUNICATION SYSTEM”, which is incorporated herein by reference. In an asynchronous HARQ protocol it is relatively straight forward to apply autonomous retransmissions since the HARQ process is explicitly signaled for each (re)transmission. The transmitter can thus, e.g., chose to send consecutive TTIs in the same HARQ process.
The HARQ protocol finally specified for E-DCH is synchronous, rather than being asynchronous. A synchronous HARQ protocol for E-DCH means that retransmissions takes place a fixed number of TTIs after the previous (re)transmission. Autonomous retransmissions are therefore not straightforward to introduce for E-DCH.
One option is to modify the HARQ protocol from a synchronous protocol to an asynchronous protocol. However, such modification from synchronous to asynchronous would require relatively large modifications in the channel structure and in the specifications, and therefore is not very attractive.
Another problem with introducing longer TTIs by concatenating several 2 ms TTIs is the ACK/NACK feedback signaling. In FIG. 1 the HARQ feedback mechanism is illustrated for an example HARQ protocol with four HARQ processes (E-DCH has eight HARQ processes). The HARQ feedback signals in E-DCH are sent a fixed time after a received TTI and the transmitter knows which HARQ process the feedback refers to based on the time of reception.
As understood with reference to FIG. 1, if a 4 ms TTI is created by repeating data in HARQ process 1 and 2, the ACK/NACK signal sent after decoding process 2 would come too late to be able to do a retransmission in the correct HARQ process. The user equipment unit (UE) would only know if it is supposed to perform a retransmission or not when process 1 has already started in the next HARQ process cycle.
What is needed, therefore, and an object of the present invention, are apparatus, methods, and techniques for providing autonomous retransmissions for the E-DCH channel.